Continuum elastic models for force transmission in biopolymer gels

Soft Matter ◽  
2020 ◽  
Vol 16 (48) ◽  
pp. 10781-10808
Author(s):  
Haiqin Wang ◽  
Xinpeng Xu
Keyword(s):  
Continuum Models ◽  
Force Transmission ◽  
Biopolymer Gels ◽  
External Forces ◽  
Cellular Forces

A review of continuum models and experiments for the transmission of external forces and internal cellular forces in biopolymer gels.

Nonlinearities of biopolymer gels increase the range of force transmission

2015 ◽  
Vol 92 (3) ◽  
Author(s):  
Xinpeng Xu ◽  
Samuel A. Safran
Keyword(s):  
Force Transmission ◽  
Biopolymer Gels

scholarly journals Conditions for optimal mechanical power generation by a bundle of growing actin filaments

2018 ◽  
Author(s):  
Jean-Louis Martiel ◽  
Alphée Michelot ◽  
Rajaa Boujema-Paterski ◽  
Laurent Blanchoin ◽  
Julien Berro
Keyword(s):  
Actin Filaments ◽  
Focal Adhesions ◽  
Mechanical Power ◽  
Biophysical Model ◽  
Physical Factors ◽  
Force Transmission ◽  
Optimum Conditions ◽  
External Forces ◽  
Proper Force

AbstractBundles of actin filaments are central to a large variety of cellular structures, such as filopodia, stress fibers, cytokinetic rings or focal adhesions. The mechanical properties of these bundles are critical for proper force transmission and force bearing. Previous mathematical modeling efforts have focused on bundles’ rigidity and shape. However, it remains unknown how bundle length and thickness are controlled by external physical factors, and how the attachment of the bundle to a load affects its ability to transmit forces. In this paper, we present a biophysical model for dynamic bundles of actin filaments that takes into account individual filaments, their interaction with each other and with an external load. In combination with in vitro motility assays of beads coated with formins, our model allowed us to characterize conditions for bead movement and bundle buckling. From the deformation profiles, we determined key biophysical properties of tethered actin bundles, such as their rigidity and filament density. Our model also demonstrated that filaments undulate under lateral constraints applied by external forces or by neighboring filaments of the bundle. Last, our model allowed us to identify optimum conditions in filament density and barbed end tethering to the load for a maximal yield of mechanical power by a dynamic actin bundle.

scholarly journals A multiscale model of mechanotransduction by the ankyrin chains of the NOMPC channel

2019 ◽  
Vol 151 (3) ◽  
pp. 316-327 ◽  
Author(s):  
David Argudo ◽  
Sara Capponi ◽  
Neville P. Bethel ◽  
Michael Grabe
Keyword(s):  
Normal Mode Analysis ◽  
Multiscale Model ◽  
Force Balance ◽  
Mode Analysis ◽  
Sensory Cells ◽  
Force Transmission ◽  
Balance Analysis ◽  
Dynamics Simulations ◽  
External Forces ◽  
Electrical Impulses

Our senses of touch and hearing are dependent on the conversion of external mechanical forces into electrical impulses by the opening of mechanosensitive channels in sensory cells. This remarkable feat involves the conversion of a macroscopic mechanical displacement into a subnanoscopic conformational change within the ion channel. The mechanosensitive channel NOMPC, responsible for hearing and touch in flies, is a homotetramer composed of four pore-forming transmembrane domains and four helical chains of 29 ankyrin repeats that extend 150 Å into the cytoplasm. Previous work has shown that the ankyrin chains behave as biological springs under extension and that tethering them to microtubules could be involved in the transmission of external forces to the NOMPC gate. Here we combine normal mode analysis (NMA), full-atom molecular dynamics simulations, and continuum mechanics to characterize the material properties of the chains under extreme compression and extension. NMA reveals that the lowest-frequency modes of motion correspond to fourfold symmetric compression/extension along the channel, and the lowest-frequency symmetric mode for the isolated channel domain involves rotations of the TRP domain, a putative gating element. Finite element modeling reveals that the ankyrin chains behave as a soft spring with a linear, effective spring constantof 22 pN/nm for deflections ≤15 Å. Force–balance analysis shows that the entire channel undergoes rigid body rotation during compression, and more importantly, each chain exerts a positive twisting moment on its respective linker helices and TRP domain. This torque is a model-independent consequence of the bundle geometry and would cause a clockwise rotation of the TRP domain when viewed from the cytoplasm. Force transmission to the channel for compressions >15 Å depends on the nature of helix–helix contact. Our work reveals that compression of the ankyrin chains imparts a rotational torque on the TRP domain, which potentially results in channel opening.

scholarly journals The Cytoskeleton—A Complex Interacting Meshwork

Cells ◽  
2019 ◽  
Vol 8 (4) ◽  
pp. 362 ◽  
Author(s):  
Hohmann ◽  
Dehghani
Keyword(s):  
Intermediate Filaments ◽  
Cellular Transport ◽  
Force Transmission ◽  
Animal Cells ◽  
Cytoskeletal Organization ◽  
Cellular Behavior ◽  
Cytoskeletal Filament ◽  
And Migration ◽  
External Forces ◽  
The Impact

The cytoskeleton of animal cells is one of the most complicated and functionally versatile structures, involved in processes such as endocytosis, cell division, intra-cellular transport, motility, force transmission, reaction to external forces, adhesion and preservation, and adaptation of cell shape. These functions are mediated by three classical cytoskeletal filament types, as follows: Actin, microtubules, and intermediate filaments. The named filaments form a network that is highly structured and dynamic, responding to external and internal cues with a quick reorganization that is orchestrated on the time scale of minutes and has to be tightly regulated. Especially in brain tumors, the cytoskeleton plays an important role in spreading and migration of tumor cells. As the cytoskeletal organization and regulation is complex and many-faceted, this review aims to summarize the findings about cytoskeletal filament types, including substructures formed by them, such as lamellipodia, stress fibers, and interactions between intermediate filaments, microtubules and actin. Additionally, crucial regulatory aspects of the cytoskeletal filaments and the formed substructures are discussed and integrated into the concepts of cell motility. Even though little is known about the impact of cytoskeletal alterations on the progress of glioma, a final point discussed will be the impact of established cytoskeletal alterations in the cellular behavior and invasion of glioma.

Simulation of three Dimensional Defect Images in Transmission Electron Microscopy

1976 ◽  
Vol 34 ◽  
pp. 470-471
Author(s):  
W. D. Cooper ◽  
C. S. Hartley ◽  
J. J. Hren
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Three Dimensional ◽  
Crystalline Lattice ◽  
Continuum Models ◽  
Thin Foils ◽  
Transmission Electron ◽  
Microscope Images ◽  
General Computer Program ◽  
General Computer

Interpretation of electron microscope images of crystalline lattice defects can be greatly aided by computer simulation of theoretical contrast from continuum models of such defects in thin foils. Several computer programs exist at the present time, but none are sufficiently general to permit their use as an aid in the identification of the range of defect types encountered in electron microscopy. This paper presents progress in the development of a more general computer program for this purpose which eliminates a number of restrictions contained in other programs. In particular, the program permits a variety of foil geometries and defect types to be simulated.The conventional approximation of non-interacting columns is employed for evaluation of the two-beam dynamical scattering equations by a piecewise solution of the Howie-Whelan equations.

FUNDAMENTALISMO RELIGIOSO CRISTÃO E ISLÂMICO: TENDÊNCIAS SOCIOPOLÍTICAS

2019 ◽  
Vol 10 (23) ◽  
pp. 073
Author(s):  
Marcio Luis Costa ◽  
Alex Silva Messias
Keyword(s):  
The Other ◽  
Religious Movement ◽  
Religious Fundamentalism ◽  
Social Phenomenon ◽  
International Level ◽  
Social Politics ◽  
Political Pressure ◽  
Historical Responsibility ◽  
The Social ◽  
External Forces

Nas últimas décadas se observa o retorno da religião sob forma de fundamentalismo religioso, utilizando a mídia e instrumentos de pressão política para fazer valer suas crenças, pois diante do receio ao questionamento, os fundamentalistas veem no “outro”, no diferente, uma ameaça a ser combatida e, em alguns casos, extirpada para preservar suas convicções. O presente estudo tem por objetivo discutir as tendências sócio-políticas do fundamentalismo religioso cristão. Para tanto, com método bibliográfico narrativo, visitamos alguns autores em nível nacional e internacional, que abordam as condições que fizeram emergir o fenômeno social do fundamentalismo religioso, sua estruturação e atuação, até suas demandas sócio-políticas. Os resultados apontam que quando se identifica e transfere qualquer responsabilidade pessoal e histórica para as forças externas, o “outro”, entendido como pessoa e/ou instituição, não podemos negar que esse processo alcança dimensões de problema social. Notamos algumas tendências como mudança de movimento religioso para ideologia acirrada, da postura de fiel para militância, do “ad intra” das religiões para demandas “ad extra”, dos altares e púlpitos para ocupações políticas.Palavras-chave: Fundamentalismo Religioso; Protestante; Católico. CHRISTIAN RELIGIOUS FUNDAMENTALISM: SOCIAL-POLITICS TENDENCIESAbstractIn the last decades the return of religion in religious fundamentalism form can be observed, using media and instruments of political pressure, because when facing the fear of questioning, fundamentalists see in the “other”, in the different, a threat to be stopped and, in some cases, extirpated top preserve their convictions.  This study aims to discuss the social-politics tendencies of the Christian religious fundamentalism. For that, with the narrative bibliographic method, we visited some authors of national and international level, that approach the conditions that caused the emergence of the religious fundamentalism social phenomenon, its structure and role, until its social-politics demand. The results show that when any personal or historical responsibility is identified and transferred to external forces, the “other”, understood as person and/or institution, we cannot deny this process reaches dimensions of social problem. We notice some tendencies such as the change of the religious movement to fierce ideology, from the posture of faithful to militancy, from “ad intra” of religions to “ad extra” demands, from the altars and pulpits to political positions.Keywords: Religious Fundamentalism; Protestant; Catholic.

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